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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Tourmaline in the Passagem de Mariana gold deposit (Brazil) revisited: major-element, trace-element and B-isotope constraints on metallogenesis

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Author(s):
Trumbull, R. B. [1] ; Garda, G. M. [2] ; Xavier, R. P. [3] ; Cavalcanti, J. A. D. [4] ; Codeco, M. S. [1]
Total Authors: 5
Affiliation:
[1] GFZ German Res Ctr Geosci, Potsdam - Germany
[2] Univ Sao Paulo, Inst Geociencias, Sao Paulo - Brazil
[3] Univ Estadual Campinas Unicamp, Inst Geociencias, Campinas, SP - Brazil
[4] Serv Geol Brasil CPRM, Belo Horizonte, MG - Brazil
Total Affiliations: 4
Document type: Journal article
Source: MINERALIUM DEPOSITA; v. 54, n. 3, p. 395-414, MAR 2019.
Web of Science Citations: 4
Abstract

Tourmaline at Passagem de Mariana forms three associations: stratiform tourmalinite (T1), wall-rock alteration around quartz-sulfide veins (T2), and clusters within the veins (T3). The major-element composition of tourmaline is similar in all, with Mg/(Mg+Fe) from 0.59 to 0.83 (mean 0.69 +/- 0.03) and total Al contents from 6.2 to 6.6 atoms per formula unit (apfu). The Y-site Al (0.2-0.6apfu) is charge-balanced by the exchange NaMg(Al?)(-1). Tourmalinite type (T1) is unzoned, whereas T2 and T3 grains display increasing Ti and Ca from core to rim. In situ trace-element analyses of T1 grains were prohibited by grain size and inclusions. The T2 and T3 tourmaline have similar trace-element values, except higher concentrations of Zn, Cu, and Co in T3, which is consistent with its location in the mineralized veins. The B-11 values of T1 and T2 tourmaline range from -17.8 to -9.7 parts per thousand, with indistinguishable mean values (-13.9 +/- 1.9 and -13.8 +/- 1.6 parts per thousand, respectively), supporting field evidence that T1 tourmalinite is hydrothermal. The B-11 values of T3 tourmaline are about 5 parts per thousand higher (mean -8.9 +/- 1.3 parts per thousand), which we ascribe to depletion of B-10 in the vein fluid due to tourmalinization of wall rocks. This implies that the initial B-11 value of hydrothermal fluid was about -11 parts per thousand (for 400 degrees C and the T1-T2 mean B-11=-14 parts per thousand). This indicates a crustal boron source but is otherwise non-specific. Based on geological arguments, we favor a source in the Minas Supergroup metasedimentary units hosting the deposit. (AU)